Pump jack



p 6, 1958 A. ANDREWS 2,852,001

PUMP JACK Filed Nov. 4, 1954 INVENTOR. l- AIbert Andrews ATTORNEY UniteA PUMP JACK Application November 4, 1954, Serial No. 466,898

12 Claims. (Cl. 121-150) This invention relates to pump jacks, used forbrevity to refer to apparatus for producing upward and downwardreciprocatory movement of a pump rod in an oil or water well, or anyother type of apparatus in which such type of movement is desired, towhich my copending application Serial No. 388,400, filed October 26,1953, also relates.

In pumping oil from oil wells, a reciprocating pump is placed in thewell at a depth such that the oil will flow into the pump and the pumpis reciprocated by means of a pump rod which extends upwardly throughthe pumping tube to the collar or top of the well. Due to the depth ofoil wells, such as from severalhundred to several thousand feet, theweight of the pump rod itself, in addition to the weight of the oil inthe pumping tube, is often considerable, such as several tons, and thisweight must be lifted at each stroke of the pump. The stroke of thepumps normally used for pumping oil wells may vary between one foot andfive feet, depending upon the lift required at each stroke to producethe desired rate of flow, and the number of strokes per minute arerelatively small, such as from five to fifteen per minute. Previously,extremely heavy and cumbersome gear driven apparatus has been used toreciprocate oil well pump rods. Such apparatus conventionally includes alarge heavy Walking beam, moved upwardly and downwardly by a crankactuated from a motor or engine through a gear train. In addition, thecrank is formed as part of or attached to a heavy counter-weight whichtends to balance the weight of the pump'rod and the oil in the well.Even with the use of a counter-weight, the force required to lift thepump rod at each stroke of the pump is considerable, and such apparatusis therefore usually quite expensive, each such apparatus or pump jackoften costing several thousands of dollars. In addition, the problems ofadequate lubrication and wear require'constant attention andconsiderable sums for upkeep.

Among the objects of the present invention are to provide a novel andimproved apparatus for producing vertically reciprocating movement,particularly a pump jack; to provide such apparatus which ishydraulically operated and thereby permits a small driving unit ofnominal horsepower to operate against the heavy but slow moving loadimposed upon the pumping rod in operation; to provide such apparatuswhich may be adjusted to any desired rate of stroke and is therebyadapted to control the rate of reciprocation of the well pump rod forany desired optimum period of time; to provide such apparatus which isespecially adapted to be mounted upon a conventional terminal T of thepumping tube; to provide such apparatus which is easy to set up andreadily adjusted for operation; to provide such apparatus which iseffective,

States Patent "ice dependable, and economical to operate and requires aminimum of maintenance; to provide such apparatus which is compact,light in weight and constructed simply of few parts so that it may beeasily disassembled for maintenance and repair; and to provide suchapparatus which is rugged and constructed so that .no parts tend to beoverstressed.

With the foregoing in view, as well as other objects which will becomehereinafter apparent, the invention comprises certain combinations andarrangements .of parts and elements as herein described and defined inthe appended claims, and illustrated in a preferred embodiment in theaccompanying drawing, in which:

Fig. 1 is a vertical section taken through the longitudinal verticalaxis of a pump jack constructed in accordance with this invention, withdifferent positions of certain movable parts indicated by broken linesand additional parts to form a more complete apparatus indicateddiagrammatically by dot-dash lines;

Fig. 2 is an upper horizontalsection, takenfrom the position of line 22of Fig. 1; and

Fig. '3 is a lower horizontal section, taken from .the position of line33 of Fig. .1.

Referring to the drawing, a pump jack constructed in accordance withthis invention is adapted to be. mounted upon the upper end of aconventional terminal T -10 of a pumping tube 11 of a well pumpingassembly, such an assembly including also a pump rod 12 extending withinthe tube 11 to a pump below .(not shown) :and a pipe 13 which isconnected to the outstanding .leg of T if) for discharging oil or waterpumped upwardly from the well through tube 11. The pump rod 12, whichmoves upwardly and downwardly within the tube 11 during operation, ispreferably of such length that it terminates within the T 10 at theupper limit of the pumping stroke, as at a coupling 14 which may .beinternally threaded for a purpose hereinafter described. Forinstallation, maintenance, dismantling or repair of the pump jack, pumprod 12 may be held at its upper limit of movement within T 10 byremoving the .pipe .13 and inserting a fork or tongs not hereinillustrated,.-into the side opening of the T 10, to engage the pump rodbelow the coupling 14.

A piston and cylinder assembly I of the pump jack includes an upstandingcylinder 20 having a suitable internal diameter and wall thickness towithstand the pressures and stresses imposed upon it with a lengthsutficient to accommodate movement of a piston 21 mounted therein. Ingeneral, asuitable hydraulic fluid is supplied at a suitable pressure atall times .to the interior of cylinder 20 and controlled .by a valve Vso that hydraulic pressure will force piston 21 upwardly during the upstroke, when the valve V is in closed position, thereby moving upwardlywith it pump rod 12 and the pump connected to the lower end of rod 12.On the down stroke, hydraulic fluid is .supplied to cylinder 20, butmerely flows therethrough with the valve V in open position, so that theweight of oil or water in tube 11 and the weight of pump rod 12 willpull the cylinder 21 downwardly, such weight producing a force tendingto move pump rod 12 in one direction. The valve V is automaticallyshifted between openand closed positions as the piston 21 reaches theend of its downward and upward strokes, respectively, .in a mannerhereinafter described.

In accordance with this invention, cylinder 20 is fixedly attached atits lower end to a base plate 22, as by being threaded on and thenwelded to an upper boss 23 thereof, while a lower boss 24, concentricwith upper boss 23, is removably attached, as by threads, in the topopening of the T 10. As will be evident, cylinder 20 is thereby axiallyaligned with the pump tube 11 and pump rod 12, while cylinder 20 andplate 22 are attachable to and removable from T as a unit.

Athreaded aperture 25, axially aligned with cylinder 20, extends throughbase plate 22 and the opposing bosses, for attachment of an axiallycentered guide tube 26 for a piston rod 27, which reciprocate in guidetube 26. The lower threaded end 28 of piston rod 27 is attached to pumprod 12 in coupling 14, while rod 27 extends upwardly into the cylinderfor connection with piston 21, as hereinafter described, therebyoperatively connecting piston 21 with the pump rod 12. Suitable O-ringgaskets 29 may be mounted within internal circumferential grooves on theinside of the upper end of guide tube 26 to prevent leakage from thecylinder through the tube 26 and past the rod 27, while the exterior ofthe upper end 30 of guide tube 26 may be hexagonal to permit a wrench tobe applied thereto. Such a wrench may be similar to the socket wrenchesutilized in turning on and off water valves and the like, which aredisposed deep within an access pipe, thus preferably having along shankso as to be insertable through the open upper end of the cylinder andprovided at its lower end with a'hexagonal socket adapted to fit overthe inner end of the guide tube and at its upper end with a handleextendingcross-wise to the shank. Due to the fact that the threadedconnection between the guide tube 26 and the 'base plate 22 is subjectedto full pressure of fluid within the cylinder 20, such as between 500and 1,000 pounds per square inch, a tight joint between guide tube 26and the threaded aperture 25 is preferably obtained so that a heavy pullis exerted in finally tightening the guide tube,

a similarly heavy pull thus being required when the guide tube isremoved. A suitable sealing compound also may be applied to the lowerend of the guide tube 26 and the threaded aperture 25, so as to providea more efiective seal.

The piston 21 preferably has a sliding fit with the cylinder 20 and ispreferably formed with a depending skirt 31, which provides sufficientbody length to increase stability and also to assist in control of theoperation of valve V, as hereinafter described, the upper position ofthe piston 21 being shown in full lines and the lower position beingshown in broken lines. The rod 27 extends within the pocket below thepiston formed by the skirt 31 and through an axial hole 32 in the bodyof the piston, being firmly seated against the piston at a shoulder 33,which cooperates with a nut 34 engaging the upper end 135 of the rod 27.The connection between rod 27 and piston may also be rendered leak-proofby a gasket type washer 36, or in any other suitable manner. The piston20 is also provided with two or more series of circumferential grooves,as adjacent each end, in which sealing rings 37 are installed. Piston 20is further provided with acircumferential groove 38 near the top for thepassage of fluid for control of the operation of valve V, as hereinafterdescribed.

that the weight of the pump rod and liquid will vary from well to welland that for relatively shallow wells counterbalancing may beunnecessary and coupling 39 and cable C may therefore be omitted.

The hydraulic fluid is supplied at a suitable pressure,

such as 500 to 1000 pounds per square inch, through a pressure line 41to the bottom of the cylinder 20, the pump 40 being shown wholly andline 41 being shown partially diagrammatically in dot-dash lines inFig. 1. Line 41 is connected to an inlet 42 of cylinder 20 byconventional fittings 43. From the cylinder 20, on the down stroke, thefluid flows through control valve V and thence through a return line 44to a fluid reservoir 45, which is interconnected with the intake of thepump 40 to complete the circuit, the line 44 and reservoir 45 also beingshown diagramatically in dot-dash lines in Fig. l. The operation of theunit is thus regulated by the control valve V, since when the valve isclosed, fluid is pumped into the cylinder to raise the piston and liftthe pump rod 12, while when the valve V is open, fluid flows from thecylinder and through the return line 44, with the weight of the pump rodand fluid pulling the piston downwardly.

The control valve V is a pressure-actuated spool valve having acylindrical body 48 closed at its lower end 49 and its upper end 50,either of which may be integral with the body and either or both ofwhich may be removable, such as the lower end cap 49 which may beremovably attached to the body 48 by threads as shown, or by cap Valvebody 48 may be mounted in an upright position in an aperture 51 in thebase plate 22 alongside the cylinder 20, or valve V may be supported inany other suitable manner, as by tubes 52 which extend between outlets53 at the lower end of cylinder 20 .and inlets 54 of valve body 50, bywhich valve V communicates with the cylinder 20. Tubes 52 may bethreaded into suitable bosses on the face of the cylinder and attachedto diametrically opposed bosses on the face of the body 59 byconventional fittings 55, the aforesaid position of valve inlets 54providing a balanced pressure on a piston or spool 56 within the body48. An exhaust passage 57 from the valve V is in radial alignment withvalve inlets 54, while an auxiliary or needle valve 58 having anadjusting screw 59 is preferably mounted upon the valve body andconnected with passage 57, with the return line 44 being connected tothe exhaust side of the auxiliary valve.

The spool 56 is adapted to move upwardly and downwardly within the body48, the spool having suitable piston rings 60 in circumferential groovesat each end to eliminate leakage, a circumferential groove 61 and asolid exterior portion 62 below the groove. Downward movement of spool56 causes groove 61 to register with the inlets 54 and exhaust passage57,'so that the valve V Will be in open position, the spool 56 thusbeing in the position shown in Fig. l. Upward movement of spool 56, tothe closed position of valve V, shifts the solid portion 62 upwardly tocover the inlet and exhaust openings, thereby restricting flow fromcylinder 20, so that substantially the full pressure of fluid suppliedby pump 40 will be exerted against piston 21, to raise pump rod 12. Aspring 63 is positioned within the body 48 underneath the spool to movespool 56 upwardly to a normally closed position, while a bleed line 64from the chamber within the body 48 below the spool is preferablyprovided to prevent an accumulation of fluid therein from interferingwith the desired movement of the spool, such line 64 being convenientlyconnected to the discharge side of the auxiliary valve 58.

To thrust the spool downwardly to open position automatically whenpiston 21 reaches the top of its stroke, a control'line 65 is connectedto a pressure control inlet 66 in the top 50 of the valve body, as byconventional fittings 67. Control line 65 extends upwardly to a checkvalve 68 which is connected to a pressure control port 69 of thecylinder 20, as by fittings 70. Pressure control port 69'is positionedat a point which will be immediately below the lower rim of the pistonskirt 31 when the piston 21 reaches its upper limit of movement, asshown in full in Fig. l, to permit a flow of pressurized fluid fromWithin the cylinder 20 through line 65 to enter the top of the valvebody 48 and depress the spool 56 against the pressure of spring 63. Thisproduces a positive movement of spool 56 downwardly to the position ofFig. 1, thereby releasing the pressure within the cylinder 20, so thatpiston 21 will start its descent. Whenever a quick release of pressurein cylinder tends to reduce the pressure in line 65 and above spool 56so that spring 63 might move spool 56 upwardly, before the skirt 31 cancover port 69 as piston 21 starts down, check valve 68 will close toprevent a return flow from the valve body 48 to the cylinder 20, therebytrapping fluid under pressure which holds the spool 56 in the depressedposition, i. e., the open position of valve V, throughout the downwardstroke of the piston.

For release of the fluid pressure above spool 56 of valve V, when piston21 reaches the lower end of its downward stroke, an exhaust control tube71, which may be considered as a continuation of the line 65, extendsfrom the check valve 68 to an exhaust control port 72 in cylinder 20above the pressure control port 69, tube 71 being connected thereto in asuitable manner, as by fittings 73. Diametrically opposite port 72 islocated another exhaust control port 74, to which a bleed line 75 may beconnected, as by fittings 76, the bleed line 75 returning to thereservoir 45. The position of the ports 72 and 74 is such as to registerwith the groove 38 on piston 21, when the piston reaches the downwardlimit of its movement, as shown in broken lines in Fig. 1. In suchposition, the line 65, tube 71, port 72, groove 38, port 74 and bleedline 75 form a direct communication from the chamber in the top of valvebody 48 to the reservoir 45, thereby releasing the pressure of fluid inthe valve body above spool 56 and permitting the spool to be movedupwardly by spring 63, to move the valve V to closed position and permitthe upward stroke of the piston to commence.

To recapitulate briefly, the operation of the pump jack of thisinvention is based upon the continuous operation of the pump to supplypressurized fluid to the cylinder 20. With the spool 56 in the upper orvalve closed position, moved thereto by spring 63, the pressure of fluidin the cylinder raises the piston 21. At the top of the piston stroke,fluid from cylinder 20 moves through port 69, past check valve 68,through line 65 and into the top of the body 48 of the valve V,depressing the spool 56. This moves the spool 56 downwardly to open thevalve and release the pressure with all fluid movement from the cylinderthen being through return line 44, while the fluid trapped in the top ofvalve V holds it in open position until the piston reaches the bottom ofthe stroke, whereupon the groove 38 registers with ports 72 and 74 toconnect line 65 and tube 71 with the bleed line 75, thereby releasingthe pressure in the top of valve V to permit the spool to be raisedagain by spring 63 to close the valve V. As will be evident, repetitionof these operations will proceed automatically. If the rate of upwardmovement of piston 21 is to be changed, a higher pressure produced bypump 40 will increase such rate, while a lower pressure will reduce it.Thus, pump 40 preferably has an adjustable outlet pressure, which may beaccomplished by utilizing a variable pressure pump or by driving thepump by an adjustable speed motor or gas or oil engine. Also, if therate of downward movement of piston 21 is to be changed, auxiliary valve58 may be opened to increase the rate, or closed to decrease it. Thus,the number of strokes per unit of time is readily adjusted. If desired,the valve V may be incorporated within the piston 21, but withoutaffecting control by the piston and particularly the movement thereof,of the opening and closing of the valve V.

The pump jack of this invention is readily assembled and disassembled,both initially and at the well. It is to be noted that the plate 22 isremovably attached to the upper end of the T 10, while the cylinder 20is preferably permanently attached. to the plate 22, as by weld- 6 ing.Also, the piston 21 is slidable through the open upper end of thecylinder 20. For assembling the-pump jack at the well, the pump rod 12may be supported in the manner described previously, i. e., by a fork ortongs, and if the piston rod 27 .is not attached to the piston, thepiston rod may be attached to the coupling 14 of the pump rod 12. Then,the cylinder 20 may be slipped'over the piston rod 27 withv the guidetube 26 sliding down the piston rod 27. Then, the plate 22 may beengaged by a suitable wrench or the like to screw the threads on thelower boss 24- into the threads at the upper end of. the T 10. Thisthreaded connection is, of'course, subjected only to the pressure offluid being pumped up from the well, so that the pressure thereagainstis not very great and a gasket or other sealing device is thereforenormally unnecessary. After the cylinder and piston rod have been thusplaced in position, the piston 21 may be slipped into the upper end ofthe cylinder until: the shoulder 33 of piston rod 27 is engaged, gasket36 conveniently being placed on the shoulder before the piston isslipped into the cylinder. Then, the nut 34 may be tightened to attachthe piston rod 27 securely to the piston 21. Or, the cylinder may beattached to the T 10 and the piston 21 and the piston rod 27, ifpreviously attached together as a unit, slipped into the piston. Theskirt 31 of the piston will hold the piston rod concentric to thecylinder 20 so that the lower end of the piston rod will readily slideinto the guide tube 26. As soon as the lower end of the piston rodcontacts the coupling 14, a wrench having a suitable extension may beinserted within the upper end of the piston to engage nut 34, to turnthe piston 21 and rod 27 as a unit and thereby screw the lower end 28 ofpiston rod .27 into coupling 14.- Similarly, when disassembling the pumpjack, as for repair, inspection or the like, the wrench may be placed onthe nut 34 to unscrew the piston 21 and rod 27 as a unit, which may belifted with the cylinder, after plate 22 is unscrewed, although if therepairs are to be made only to the piston 21, such as the replacement ofone or more of the piston rings 37, the cylinder 20 may be left inplace. However, if the O-rings 29 require replacement, the cylinder 20may be removed by unscrewing the plate 22 from the T 10, after which theguide tube 26 may be removed and the sealing rings repaired or replaced.As will be evident, the valve V may remain attached to the cylinder 26when the plate 22 is screwed into or out of the T 10, since the pipe 13will have been removed to permit the fork or tongs to support the pumprod 12 and the valve V will clear the fork or tongs during rotation ofthe cylinder 20. Thus, the only connections necessary to take apart,when disconnecting the cylinder from the pump rod assembly, are merelythe'pressure supply line 41, the return line 44 and the bleed returnline 75, which may readily be disconnected by detaching the fittings bywhich the first two are connected to the cylinder 20 and detaching aunion which is preferably installed in line 44 adjacent valve 58. In theevent that. a number of pump jacks are in operation, it may bedesirable, whenever one of them needs attention, merely to substituteanother pump jack for the one to be inspected or repaired. Due to thefact that the lines 41, 44 and 75 are readily disconnected and theentire pump jack then may be removed merely by unscrewing piston rod 27and plate 22, such an exchange operation may be done in a matter of onlya few minutes, thereby preventing the well from being shut down for anyperiod of time.

From the foregoing, it will be evident that a pump jack constructed inaccordance with this invention fulfills to a marked degree therequirements and objectshereinbefore set forth. As will be evident, sucha pump jack is hydraulically operated and is adapted to be utilized forreciprocating a pump rod in an oil or water well. Since the usual rateof reciprocation of pump rods is normally relatively slow, a hydraulicpump requiring only a relatively small horsepower 'motor or engine todrive the same may be utilized to actuate the pump jack. Due to thepositive movement of the control valve by the springs in one directionand by full hydraulic pressure in the opposite direction, and furtherdue to the locking of pressure in the valve in the open position, theaction of the pump jack is effective and certain. As describedpreviously, the number of'strokes per unit of time is readily adjusted.Due to the fact that when the cylinder and piston rod are accuratelycentered with respect to the pump rod, the lateral stresses on thehydraulic piston and cylinder are minimized. By using comparatively highhydraulic pressures, such as up to 1,000 pounds per square inch, a largeupwardly directed force can be produced without requiring extremelyheavy operating parts. As will be evident, the pump jack may readily bedisassembled for repair or inspection. Also, all of the parts may bereadily handled by one workman, in the manner described. Due to morecertain and effective operation and also due to the fact that thehydraulic fluid may act also to lubricate the moving parts, the pumpjack of this invention tends to require a minimum of attention andupkeep. As will also be evident, the pump jack may be made from readilyprocurable parts at a reasonable cost.

Although a specific embodiment of this invention has been described andillustrated, it will be understood that other embodiments may exist andthat various changes may be made, without departing from the spirit andscope of this invention.

What is claimed is:

1. Apparatus for producing upward and downward reciprocatory movement ofa pump rod in an oil well and the like, said pump rod being subject to aforce tending to move said pump rod in one direction, comprising acylinder mounted in substantial alignment with the pump rod; areciprocable piston within said cylinder; a piston rod connected to saidpiston; means connecting said piston rod with said pump rod; means forcontinuously supplying fluid under pressure to the interior of saidcylinder between said piston and one end of said cylinder; meansincluding a valve for controlling the flow of fluid from said cylinder;and at least partly hydraulic means operable in response to the movementof said piston for controlling said valve and constructed and arrangedto close said valve when said piston nears said cylinder end and therebypermit fluid flowing into said cylinder to move the piston away fromsaid end and move said pump rod in a direction'opposite to said force,and to open said valve when the piston moves a selected distance withinthe cylinder to permit such force on said pump rod to move the pistonback to the initial position near said end of said cylinder.

2. Apparatus as defined in claim 1, wherein said valve control meansincludes a port in the wall of said cylinder and cooperating with saidpiston.

3. Apparatus as defined in claim 1, wherein said valve includes a.cylindrical body and a spool movable axially therein, intake anddischarge ports in radial alignment in said body, a circumferentialgroove in said spool movable into alignment with said ports at oneposition of the spool and an exteriorly solid portion spaced from saidgroove and adapted to close said ports at another position of saidspool.

4. Apparatus as defined in claim 3, wherein said control means includesa compression spring within said valve body at one end of said spool fornormally shifting said spool to a position closing said ports; and afluid line to said body at the other end of said spool and connectedwith a port in said cylinder at a point remote from said closed .end,said port being closed by said piston until said piston has moved to theend of its stroke in a direction away from said one end.

5. Apparatus as defined in claim 4, including a check valve in saidfluid line adapted to prevent a return flow from said valve body as thefluid pressure drops within said cylinder responsive to the opening ofsaid valve.

6. Apparatus as defined in claim 4, wherein said cylinder is providedwith spaced ports; said fluid line is connected also to one of saidports; an exhaust line is connected to another of said ports; andsaid'piston is provided with a groove connecting said ports when saidpiston reaches the end of its stroke adjacent said one end.

7. Apparatus for producing upward and downward rcciprocatory movement ofa pump rod in an oil well and the like, said pump rod being subject to aforce tending to move said pump rod in one direction and said pump rodbeing movable vertically in a tube having a terminal T at the topthereof, comprising a base plate removably mounted upon said T; acylinder upstanding from and attached to said base plate in substantialaxial alignment with said pump rod and having an inlet at the bottom andan outlet; a guide tube upstanding from said base plate within saidcylinder and having a passageway therethrough; a piston within saidcylinder; a piston rod extending through said guide tube and connectingsaid piston and said pump rod, said guide tube having sealing means forsaid piston rod; means for continuously supplying fluid to said cylinderinlet at the bottom thereof; a valve for controlling flow of fluid fromsaid cylinder outlet; and means for opening and closing said valve inresponse to the position of said piston in said cylinder.

8. Apparatus as defined in claim 7, wherein said base plate isthreadedly attached to said T and said cylinder is Welded to said baseplate.

9. Apparatus for producing upward and downward reciprocatory movement ofa pump rod in an oil well and the like, said pump rod being subject to aforce tending to move said pump rod in one direction, comprising acylinder mounted in substantial alignment with the pump rod and havingthe end adjacent to said pump rod closed except for a central passagetherethrough; a reciprocable piston Within said cylinder; a piston rodslidably extending through said passage and connecting said piston withsaid pump rod; means for continuously supplying fluid under pressure tothe interior of said cylinder between said piston and said closed end;means including a valve movable to different positions for controllingthe flow of fluid from said cylinder; and means operable'in response tothe movement of said piston for controlling said valve, and constructedand arranged to close said valve when said piston nears said cylinderclosed end and thereby permit fluid flowing into said cylinder to movethe piston away from said end and move said pump rod in a directionopposite to said force and to open said valve when the piston moves aselected distance within the cylinder to permit such force on said pumprod to move the piston back to the initial position near the closed endof said cylinder, said means including a port in said cylinder forsupplying fluid pressure to said valve for moving said valve to oneposition and hydraulic means cooperating with said piston for releasingsuch pressure so that said valve can move to the opposite position.

10. Apparatus as defined in claim 9, wherein said hydraulic meanscooperating with said piston includes spaced ports in said cylinder incircumferential alignment and a circumferential groove in said cylinderdisposed to connect said spaced ports when said piston moves to apredetermined position.

11. Apparatus as defined in claim 9, wherein said valve control meansincludes a port in the Wall of said cylinder which is uncovered by saidpiston for supplying fluid pressure to said valve for moving said valveto said one position.

12. Apparatus for producing upward and downward reciprocatory movementof a pump rod in an oil well and the like, said pump rod being subjectto a force tending to move said pump rod in one direction, comprising acylinder mounted in substantial alignment with the pump rod and havingat one end hereof an inlet and an outlet spaced from said inlet; areciprocable piston within said cylinder; a piston rod connected to saidpiston; means connecting said piston rod with said pump rod; means forcontinuously supplying fluid under pressure to the interior of saidcylinder at said inlet and between said piston and said one end of saidcylinder; means including a valve for controlling the flow of fluid fromsaid cylinder outlet; and at least partly hydraulic means operable inresponse to the movement of said piston for controlling said valve andconstructed and arranged to close said valve when said piston nears saidcylinder end and thereby permit fluid flowing into said cylinder to movethe piston away from said end and move said pump rod in a directionopposite to said force, and to open said valve when the piston moves aselected distance within 10 the cylinder to permit such force on saidpump rod to move the piston back to the initial position near said endof said cylinder.

References Cited in the file of this patent UNITED STATES PATENTS1,053,032 Harris Feb. 11, 1913 1,910,644 Smith May 23, 1933 2,048,550Helenberg July 21, 1936 2,157,219 Salentine May 9, 1939 2,578,204 PeekDec. 11, 1951 2,583,285 Zehnder Jan. 22, 1952 2,650,574 MacDonald Sept.1, 1953

